Keg Purge Thought Experiment

Dave, I would be interested in hearing your results. It is my guess that it would take quite some time before the vast majority of the gas at the bottom is CO2 but if you have the ability to conduct this experiment that would be great!

Cheers!

Jack

 

Purge from the dip tube. I have been thinking about that.

 

This is not consistent with how Molecular Diffusion works. If denser gases always settled to the bottom our earth's atmosphere would consist of a thin layer of xenon (molecular weight of 131) on the surface with a layer of kyrpton (83) above that, followed by a layer of carbon dioxide (44), then you would reach a large band of oxygen (32). Not until you went many miles up would you encounter the first molecule of nitrogen (28) and wouldn't expect to see a trace of hydrogen (2) until you were on the edge of outer space. But in actuality the composition of atmospheric air is homogeneous . . . the same ratios of these gases exist at sea level as on the top of Mt Everest.

Breathing gases are routinely mixed into cylinders (shaped similar to a keg) with different weight gases and they mix and are breathed in an equal ratio. Heliox (US Navy) is a mix of helium (4) and oxygen(32) that is blended into a cylinder. Once they have mixed the first and last breath will be identical ratios of the two gases. Recreational divers regularly use Nitrox (N2O2) or Trimix (N2O2He) in the same manner. I've added helium to a tank of N2O2 and it "sinks" (diffuses) to the bottom for a homogeneous mixture. This is all confirmed with a gas analyzer. This isn't confined to breathing gases, any element in a gaseous state will behave in accordance with the Gas Laws.

That said, the mixing isn't instantaneous . . . time required is based on molecular weight and temperature and the math can be daunting. But it does occur . . . gases always move from a higher concentration to a lower concentration until they reach equilibrium. Something like a fuel spill or a catastrophic release of toxic gases would be a danger until they diffused and you would want protection before wading in.

 

But that CO2 blanket is still going to protect the beer in my fermenter, right? <d&r>

 

I don't claim to be evenly slightly knowledgeable about gasses or vapor density, but I'll throw my method into the mix to see what everyone thinks.
I fill my keg as high as possible with starsan. Give the head space a few good purges, then crank the Co2 to about 5 psi and push the starsan out through the liquid side until the keg is empty. I know there will be some residual O2 left from the headspace, but this is the best method I have come up with. I want to eventually make a racking system where I can pump beer in through the dip tube while opening the PRV to vent. I have been racking my brain lately (No pun intended) to try and come up with a way to limit dissolved O2 in my IPA's as much as possible.

 

Pretty much...that's why standard fermentation/racking techniques that have been around for years result in very drinkable beer

 

Gotta love it when brewing techniques defy the laws of physics.

 

I didn't invent the brewing techniques, but they seem to work within the laws of physics...cheers

 

My point is that CO2 "blankets" don't keep beer O2 free. People may think they do, and their beer may be quite drinkable, but that drinkability doesn't mean the CO2 kept the beer O2 free, which is impossible.

 

Exactly...and why closed purging systems are pretty much a waste of time if one is just minimally careful using "old school" techniques of purging/racking/handling, imho.

 

Closed transfers prevent (or greatly reduce) the introduction of additional O2 (above whatever the magic CO2 blanket and semi-permeable airlock setup did not prevent). That's still going to result in less total O2 than an open transfer. Add a more closed fermentation (replace traditional airlocks/blowoffs with a better PRV) and you can also avoid an airlock becoming a two way highway between the air and the beer.

Open-Rack as carefully as you want. Unless you're going to argue that less O2 is not better than more O2, there are better (more effective) ways than the most common ways. The fact that someone can make good beer with simpler methods doesn't make more advanced methods a waste of time. They are certainly more expensive, which means each brewer should evaluate the tradeoffs in their own context.

I think we got derailed here. Mostly, I'd be ecstatic if lots of people would stop thinking CO2 acts like a stainless steel bulkhead.

 

Likewise, folks that use "advanced" methods should not expect vastly improved beer if they were competent in their primitive techniques to begin with...imho.

 

If by vastly you mean going from average to awesome with just that one change, I would agree. I would say all the little things add up, and this is another one of those things. I suspect maximum O2 exclusion is much like kegging, in that people who have made the switch tend not to go back.

I feel like I was competent with traditional techniques. Competition results supported that feeling. But I'm convinced my beers are better now. Otherwise, I would go back, because it's easier.

 

By convinced, do you mean they taste better or last longer?

 

Fresh aroma and flavor last longer. Maybe taste/smell better initially (after fermentation and carbonation) too, but if so, that's more subtle.

Staling reactions begin as soon as there is more O2 than the yeast can use. It's just a question of when it becomes detectable, which probably varies from person to person, and of course how much O2 was present. To be fair, the results of staling reactions can also be perceived as positive, depending on degree, personal preference, style, and what have you. A bit of oxidation in a Barleywine or RIS can be a good thing.

 

Can you quantify those observations? Maybe my palate is not as sophisticated as some, but my kegs of IPA seem to hold up for months if kept at keggerator temps. I'm starting to think the differences might be analogous to the differences between red and white wheat (very little).

 

I can't tell the difference between beers made with moderate amounts of red wheat vs. white wheat. But I can tell my O2 excluded beers have that just-tapped hop freshness for longer. All I can say is that the drop-off at, say, 3, 4, or 5 months is noticeably less than it was before. Other people have noticed it too. Maybe it buys double the time. It's hard to say. The only way I can think of to truly quantify it would be to do A/B sensory panel testing, and that's not likely to happen.

I hear what you're saying about (non O2-excluded) IPAs holding up for months. Plenty of ribbons have been won with those. It would be nice if O2 exclusion techniques were cheap and easy. Then more people would try them and could decide for themselves.

 

I'll concur with the easy part, but if you are already kegging, there's not that much additional expense...it's just the added time and hassle for little return (unless you plan on keeping your IPA for 6 months)...imho.